1. Field of the Invention
The present invention relates to a back-light apparatus for a liquid crystal display device. More particularly, the present invention relates to a back-light apparatus for a liquid crystal display device that supplies light to a liquid crystal display panel through a plurality of light emitting diodes (LED).
2. Discussion of the Related Art
A liquid crystal display (LCD) is a display apparatus in which data signals, including image information, are individually supplied to pixels arranged in a matrix, and optical transmittance of the pixels is controlled to display a desired image. Accordingly, the LCD includes a display panel in which pixels are arranged in a matrix and a driving part for driving the pixels.
The display panel includes a thin film transistor array and a color filter substrate which are attached together to face each other with a certain cell-gap therebetween and a liquid crystal layer formed between the attached color filter substrate and thin film transistor array substrate.
A common electrode and a pixel electrode are formed in an LCD panel formed by attaching the thin film transistor array substrate and the color filter substrate together and applying an electric field to the liquid crystal layer.
If voltage of a data signal is applied to the pixel electrode and the common electrode, liquid crystal of the liquid crystal layer is rotated by its dielectric anisotropy according to an electric field between the common electrode and the pixel electrode. Accordingly, light is transmitted or cut off pixel by pixel so that text or an image is displayed.
Additionally, the LCD cannot emit light by itself and displays an image by controlling the optical transmittance. For this reason, the LCD requires a special apparatus for radiating light to a display panel, that is, a back-light apparatus.
The back-light apparatus is divided into a side type and a direct type. As for the side type back-light apparatus, a lamp is located at one or both sides of a display panel, and light is reflected, diffused and concentrated through a light guide, a reflector and optical sheets. With regard to the direct type back-light, a lamp is located at a back surface of the display panel so that light is directly transmitted to the entire surface of the display panel.
The side type back-light apparatus and direct type back-light apparatus will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is an exemplary view showing a general side-type back-light apparatus.
FIG. 2 is an exemplary view showing a general direct-type back-light apparatus.
FIG. 3 is an exemplary view showing a lamp which is used in the general side-type back-light apparatus or in the general direct-type back-light apparatus, in detail.
In FIG. 1, the general side type back-light apparatus includes a light guide 110 located on a back surface of a display panel; a lamp 120 located at a side of the light guide 110; a reflector 130 located at a back surface of the light guide 110; a lamp holder and a lamp reflector 121 fixing the lamp to the side of the light guide 110; and a line 122 for supplying power to the lamp 120.
Light generated from the lamp 120 is incident upon a side of the light guide 110 made of a transparent material. The reflector 130 located at the back surface of the light guide 110 reflects light that is transmitted to the back surface of the light guide 110 to an upper surface of the light guide 110, thereby reducing light loss and improving uniformity. Accordingly, together with the reflector 130, the light guide 110 transmits light that is generated from the lamp 120 to the upper surface.
In FIG. 2, the direct-type back-light apparatus includes a reflector 230 located at a back surface of a display panel; a plurality of lamps 220 disposed on the reflector 230 and producing light incident upon an entire back surface of the display panel; a diffusion plate 250 covering the lamps 220 and diffusing light generated from the lamps 220; and lines 220 supplying power to the lamps 220.
In FIG. 3, a cold cathode fluorescence lamp (CCFL) having a tube shape with a length corresponding to a distance between the long sides or short sides of the display panel is used as the lamp 120, 220 for the side-type back-light apparatus or the direct-type back-light apparatus. The CCFL generates white light by power supplied through the lines 122, 221 positioned.
Because mercury used as a fluorescent material in the CCFL is harmful to a human body, the CCFL does not meet stricter environmental regulations.
Additionally, in order to improve transmittance and a color reappearing rate of an LCD, an LCD using a time-division method has been actively developed. In the time-division method, one frame of an image is time-divided into first to third sub frames, and red, green and blue light is sequentially supplied according to the first to third sub-frames. However, a back-light apparatus using the CCFL is restricted in its useful range for an LCD adopting the time-division method.